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Monitoring the concentration of singlet oxygen and other free radicals in both intracellular and extracellular environment is of paramount importance, especially during therapy e.g., photo-dynamic, cold-plasma and radiation therapy. Singlet oxygen is one of the most cytotoxic reactive oxygen species and its intracellular measurement is challenging, particularly due to its short lifetime. Here we present poly-lactic-co-glycolic acid and polyacrylamide-based nanoparticles, with hydrophobic core, containing singlet-oxygen-sensor-green (SOSG), a membrane impermeable fluorescent dye, for measuring singlet oxygen in both aqueous phase and inside mammalian cells. The increase in fluorescence intensity of the dye at ~530 nm is directly proportional to the singlet oxygen concentration. The small size of the nanosensors (50–70nm) enables efficient cellular uptake, thus facilitating intracellular measurement of singlet oxygen using fluorescence microscopy. The polyacryamide nanosensor were used for monitoring intracellular singlet oxygen during plasma therapy, using room temperature helium plasma. Plasma sources produce a range of free radicals and has been utilized for various bio-medical applications, however its interaction with mammalian cells is not well studied. We characterize the changes in intracellular oxidative and toxicity till the cells become necrotic. These nanosensors provides an insight into the fundamental interaction of plasma with cells, thereby aiding in optimizing the therapeutic process.
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